I generally find that, if decoying, any cartridge which goes bang does the job!
One of my best days was using 1oz loads in 6's.
I had 82 for 102 spent carts
Everything 'worked' that day and the pigeons decoyed really well!
That was in the days before 'magnets' I only had a WAGBI Seamark flapper and home made shell deeks!
Someone 'borrowed' the flapper 'to make a pattern' and I never got it back! (must have worked for them as well)
Would like to find another one!
Have used 7.5 trap loads 6's 5's as well all to good effect.